1. Field of the Invention
The present invention relates to apparatus for handling molds used for molding articles from flowable plastic materials. More particularly, the present invention relates to apparatus for handling large molds such as are used in connection with reaction injection molding machines, the apparatus serving for selectively opening and closing cooperating mold portions that together define a cavity within which the molded article is to be formed. Additionally, the apparatus permits pivotal movement of the respective mold members to facilitate access to the article-defining surfaces of the molds, and also to facilitate removal from the mold of a formed article.
2. Description of the Related Art
The molding of large automobile body parts, such as front or rear bumpers or the like, requires very large and very heavy molds, as compared with the usual molds for the more commonly found, smaller injection molded articles. Moreover, the materials from which such automobile body parts are often made is a polyurethane material that is introduced into the mold cavity as a liquid and is prepared as a mixture of a polyol and an isocyanate. Such materials are introduced into a mold cavity under substantially lower pressures than are conventional thermoplastics, such as polyethylene or polypropylene, that are commonly used in an injection molding machine. For example, molding pressures in a reaction injection molding machine are such that the forces necessary to hold the mold portions together are frequently of the order of about 100 tons or so, whereas injection molding machines in which plasticated material is injected under a very high pressure, sometimes require mold closing forces of the order of about 3000 tons or so.
One form of mold handling apparatus for such reaction injection molding machines is shown and described in U.S. Pat. No. 3,981,671, which issued Sept. 21, 1976, to Bobbie Lee Edwards. That Edwards patent is commonly owned by the assignee of the present application, and it discloses a mold handling system in which a pair of molds are arranged one above the other adjacent the facing ends of a generally C-shaped frame, and wherein each of the molds is pivotable about its own horizontally extending pivot axis.
The Edwards patent also discloses pivoting the entire apparatus about a horizontal axis so that the molds are movable toward and away from each other in a horizontal direction. Although the apparatus disclosed in that patent is eminently suitable for its intended purpose, it results in a rather large and a tall machine, which in its vertical orientation of the molds requires lifting of very heavy mold members. Further, in its horizontal configuration the mold members are at an elevation above the ground that renders it difficult and inconvenient to remove a molded article from the mold.
Another form of mold handling apparatus for a reaction injection molding machine is illustrated and described in U.S. Pat. No. 4,708,625, which issued on Nov. 24, 1987, to Donald P. Arend. That patent discloses an arrangement wherein the molds are positioned for horizontal movement relative to each other, and each mold supporting structure is pivotally arranged to pivot about a vertical axis. One of the mold handling portions of the apparatus includes an hydraulic drive arrangement for moving its associated mold portion toward and away from the other mold portion. However, the apparatus disclosed in the Arend patent is also large and cumbersome, and it also requires the movement of large and heavy structural mold support elements of the device, which requires considerable power and high capacity drive motors. As a result, movement of the mold portions in the Arend device is slow because of the high inertia of the parts to be moved.
It is an object of the present invention to provide a mold handing apparatus for a reaction injection molding machine that permits more rapid movement of the mold members to reduce the time for completing a molding cycle.
It is a further object of the present invention to provide a mold handling apparatus for a reaction injection molding machine in which the mold members are each pivotable relative to each other and readily accessible to a machine operator.
It is a still further object of the present invention to provide a mold handling apparatus for a reaction injection molding machine in which the mold portion that carries the molded article after its formation can be rapidly pivoted toward the machine operator to facilitate rapid removal of the molded part from the mold.